This invention relates to a method and apparatus for transmitting and receiving a digital data signal in a digital data communication system, such as a local area network (LAN), or the like.
Among the apparatus for handling and receiving speech signals or audio signals, there is video equipment, such as a television, or audio equipment, such as a radio, CD player, MD player or a video tape recorder (VTR) As a method for communication of signals employed in such apparatus, such as a video tape recorder (VTR), with other equipment, a serial digital interface (SDI) format is proposed by the Society of Motior Picture and Television Engineers (SMPTE) in Proposed SMPTE Standard for Television-10-bit 4:2:2 Component and 4fsc Composite Digital Signals Serial Digital Interface (SMPTE-295M, 1994 Revision-Seventh Draft, Feb. 16, 1994) as a standard for digital audio and video signals. This SDI standard is basically a standard for signals governed by D-1 or D-2 formats for digital signals. The disclosure of Proposed SMPTE standard SMPTE-295M is hereby incorporated herein by reference.
FIG.1 shows a schematic arrangement of the SDI format which represents the application of D-1 format signals.
An upper part of FIG.1 shows a frame format of a frame made up of 1716 samples in the horizontal direction and 525 lines in the vertical direction. Digital video signals are placed in a first field active video section AVC1 of 1440 horizontal samples and 244 vertical lines and a second field active video section AVC2 of 243 lines. Specifically, the first field active video section AVC1 is a digital video signal of odd fields and the second field active video section AVC2 is a digital video signal of even fields. Ahead of the first field active video section AVC1 and the second video active section AVC2 are respectively inserted 9-line vertical blanking section VBK1, VBK2 and 10-line optional blanking sections OBK1, OBK2. Ahead and back of the first field active video section AVC1, second video active section AVC2, vertical blanking sections VBK1, VBK2 and the optional blanking sections OBK1, OBK2 are inserted a 4-sample start synchronization code SAV indicating the start of an active line and a 4-sample end synchronization code EAV indicating the end of the active line- Between the start synchronization code SAV and the end synchronization code EAV are placed 268 samples of an ancillary data section ANC which are ancillary data for horizontal blanking. A mid part of FIG. 1 indicates a signal of a frame format shown at the upper part of FIG. 1 in a line format having a width of 10 bits. For transmitting signals of the SDI format, parallel/serial conversion and encoding of the transmission channel are carried out as shown at a lower part of FIG. 1, and the signals are transmitted as serial signals having a data rate of 270 Mbps.
Although data transmission by the SDI format is achieved at a high speed, the SDI format is not suited as a transmission channel for variegated data, while it is possible to transmit: only a limited type of data (information). Specifically, the data sorts capable of being transmitted include one channel of picture signals( or video signals) and 8 channels at most of speech signals (or audio signals) as the base band digital audio signals. Thus the SDI format is not suited to transmission and reception of plural channels of the same sort of data or channel multiplication for coping with transmission and reception of plural sorts of data. On the other hand, data other than picture signals or speech signals are transmitted over a physically separate channel. In addition, the SDI format basically takes account only of one-to-one unidirectional data transmission.
In general, when simultaneously transmitting plural sorts of data, the method of providing a data transmission channel for each data sort is simple and easy, it being unnecessary to carry out data processing for transmitting excessive data. However, this presents a problem in efficiency and economic profitability in connection with cost involved in the entire data transmission system, cost involved in the data transmission channel, or labor in maintenance or extendibility of the data transmission system.
In local networks employed in data communication (LUN) especially in information processing equipment, data communication channels, such as Ethernet or token ring, have become popular in use. However, such data communication channel inherently has been developed as a data communication channel handling temporally discrete data, such as packet data employed for an electronic computer, while it is not suited as a transmission channel for temporally continuous data, such as picture/video or speech/audio signals, which-require maintenance of a temporal relation between the transmitting and receiving sides. On the other hand, the data transmission rate of the data communication channel is rather low and is not suited to transmission of picture signals which require wide frequency range, or bandwidth.
The technological tendency in the near future is to digitize all kinds of the information, inclusive of the picture/video and speech/audio data, and to treat the information simply as a bitstream irrespective of the data type. Above all, in the future digital integrated network, exemplified by the AM technique, all kinds of data are transmitted as a multiplexed bitstream. If such technical tendency is taken into consideration, the SDI format currently standardized for picture signal transmission is not fully satisfactory, while there lacks at present a particular data format for multiplexing and transmitting various data and control signals among plural communication equipment.
In view of the foregoing, it is an object of the present invention to provide a method and apparatus for transmitting and receiving a digital signal, whereby plural sorts, or types, of picture/video and speech/audio signals and the like may be transmitted as one bitstream.
In one aspect, the present invention provides a method for transmitting a digital signal in which a digital signal format of a transmitted digital signal is constituted by a first data portion made up of digital video data, a start synchronization code and an end synchronization code for bit synchronization for the first data portion, and an auxiliary data portion located between the starts synchronization code and the end synchronization code and which is made up of plural split areas. Each of the split areas of the auxiliary data portion contains at least one of a type area indicating the data type, a byte count area indicating the data volume and a data area which is a second data portion made up of digital audio data.
At the leading end of the auxiliary data portion, there is provided a line number area indicating the line number of the data.
The auxiliary data portion contains an error correction code for detecting and correcting errors in data of the type area and the byte count area.
The first data portion is made up of digital video data of a plurality of channels and the second data portion is made up of digital audio data of plurality of channels. Of course, the first data portion could also constitute audio data or other data. Likewise, the second data portion could constitute video or other data. The digital signal format contains transmission data and reception data used to identify and characterize the format and nature of the data being transmitted.
In another aspect, the present invention provides an apparatus for transmitting a digital signal having a plurality of data outputting media sources, a plurality of delay adjustment units for respectively adjusting the delay of the data from said media sources, a plurality of rate converting units for converting the data transmission rate of the respective data from the rate converting units into a transmission rate of a transmission channel, a plurality of attribute information processing units for appending the attribute information to the respective data from the rate converting units, a multi-media switching unit for optionally selecting data of the respective media sources from the attribute information processing units, a transmission controlling unit for controlling the delay adjustment units, rate converting units, attribute information processing units and the multi-media switching unit, and a multiplexing unit for multiplexing plural data from the multi-media switching unit.
In a still another aspect, the present invention provides a device for receiving a digital signal having a demultiplexing unit for demultiplexing plural multiplexed data into media source based data, a demultiplexed media switching unit for switching plural data from the demultiplexing unit into respective suitable media channels, a plurality of attribute information processing units for processing the plural data switched by the demultiplexed media switching unit based upon the attribute information for these data, a plurality of rate converting units for converting the transmission rate of the respective data from the attribute information processing units into the playback rate for data reproduction, a plurality of delay adjustment units for adjusting the respective data from the plural rate conversion units into optimum delay amounts, and a plurality of media reproducing units for respectively reproducing the data from the delay adjustment units.
In yet another aspect, the present invention provides a digital signal transmission and reception device having the above-mentioned digital signal transmitting device and the above-mentioned digital signal receiving device on the signal transmitting and signal receiving sides, respectively.
With the method for transmitting the digital signal according to the present invention, the digital signal, such ask digital video data or digital video data, is transmitted in a digital signal format interchangeable with the SDI format of the conventional digital signal transmitting method, that is a digital signal format having a first data portion made up of digital video data, a start synchronization code portion, an end synchronization code portion, and an auxiliary data portion. Each of the split areas of the auxiliary data portion contains at least one of a type area indicating the data type, a byte count area indicating the data volume, and a data area which is a second data portion made up of digital audio data. At the leading end of the auxiliary data portion, there is provided a line number area indicating the line number of the data, while the first data portion is made up of digital video data of plural channels and the second data portion is made up of digital audio data of plural channels.
With the method for-transmitting the digital signal, data from plural media are transmitted in the above-defined digital signal format. The transmitted data is received by a digital signal receiving device where data from plural media are reproduced.
The digital signal format proposed by the present invention assures upward compatibility with respect to a device for transmitting and receiving data of the conventional SDI format and hence has affinity, or compatibility, to the existing digital signal transmission system. In addition, past network resources may be directly exploited, while any newly arising cost may be minimized and the equipment employing the conventional SDI format may be introduced into another sort of network. It is also possible to interconnect a system exploiting the present digital signal transmitting method, a network or system such as existing computer network and an integrated digital network such as future ATM network in order to effect digital signal transmission between the interconnected systems.
By providing a line number area indicating the data line number at the leading end of the auxiliary data portion, an optional number of line numbers can be set, so that asymmetrical digital signal transmission, such as 1:n transmission, becomes feasible in addition to the conventional 1:1 digital signal transmission.
By providing the auxiliary data portion having error correction code for error detection and correction for the type area data and the byte count area data, digital signals may be transmitted more correctly.
The first data portion is made up of digital video data of plural channels and the second data portion is made up of digital audio data of plural channels, so that multi-channel transmission of plural media data inclusive of encoded data may be realized on a sole transmission channel.
The digital signal format contains both the data for transmission and data for reception, so that sole media data may be bi-directionally transmitted by serial digital communication.
With the digital signal transmission device and the signal reception device of the present invention, the conventional SDI format employed in video equipment may be extended to a more variegated communication system for general digital data inclusive of base-band audio data and video data, thus enabling more general digital communication. Since communication of plural media data is physically possible by a sole communication medium, system flexibility and hence system maintenance and management such as network modification may be improved significantly.
With the digital signal transmission/reception device of the present invention, since the arrangement of the digital signal reception device and that of the digital signal transmission device may be combined together, interconnection with a digital data network, such as an external computer, or a digitized public network, such as ISD, as well as with a network between existing video equipment, may be facilitated, thus allowing it to realize reciprocal communication between all sorts of media easily and broadly. This provides a more intimate relation between networks and more efficient integration, separation, editing, management:, maintenance and retrieval of plural media efficiently and in a short time irrespective of the contents of digitized data, thus enabling more flexible long-term network construction.